1. Field of the Invention
The present invention relates to a system and method for high quality image reproduction. In particular, the invention relates to a system and method wherein received image-representing signals are processed to obtain resulting processed data, the resulting processed data is stored, the data thus stored is selectively read out in accordance with operator controlled inputs, and the data thus read out is utilized, in accordance with a gray line printing technique, to produce a high quality reproduction of the original image.
2. Description of the Prior Art
There has been an increasing need, in recent years, within various medical, scientific and technical disciplines, for a technique and system for high quality image reproduction. Until now, the need for such an imaging technique has been satisfied by systems and methods which are slow, often inaccurate, costly and inefficient, and which produce image reproductions of less than adequate quality. Such systems of the prior art have also been limited insofar as capabilities are concerned and lacking in flexibility.
In one such system of the prior art, image reproduction has been accomplished through the use of negative type film (such as silver-based negative type film). The film is loaded into a cassette (typically, an 8.times.10 cassette), and the cassette is then loaded into an imaging device. Within the imaging device, a TV monitor is positioned at a specific focal distance from the plane of the film, with an objective lens being positioned in the space therebetween, this intervening space also constituting an ether. The TV monitor is connected to a conventional TV camera, the latter scanning the image or object to be reproduced.
Once the contrast, brightness, the F stop of the lens and the exposure time are adjusted, the picture is transmitted through the ether to the film plane where excitation of the silver molecules on the film takes place, and the resultant latent image is recorded permanently within the molecular substructure of the film. The film is then, after a routine exposure procedure, removed from the imager (whether physically by the operator or mechanically by a machine), and is taken to a developing station, where it is subjected to typical photographic developing techniques. Such typical photographic developing techniques may be automated (as is typically the case in photographic processing laboratories), but in any event the film is developed, fixed, stopped, dried and delivered to the technician in finished form. The latter process requires a rather long time period (anywhere from three minutes to five minutes, depending upon the particular film processing/developing technique utilized), and also requires a great deal of heat, electrical energy and chemical supplies to process the film, as well as a good deal of manual activity by the operator.
In such a technique of the prior art, the silver base of the film is often recaptured (by some chemical means), and can be resold. Although this recapturing of the silver base does supply the user with some small offset in the cost of the overall system, the recapturing process is itself very inefficient and costly, as is the operation and maintenance of the overall system.
In such a system of the prior art, the processed film must then be viewed by a light transmission technique; for example, the film is hung on an equal density view box and light is passed therethrough, so that interpretations can be made by appropriate personnel (doctors, scientists, or the like) by viewing the light patterns resulting from the transmission of light through the film.
Another significant disadvantage of such a system relates to the high price of film, the cost of which is ever increasing. In fact, at present, the cost of film is such as to render a large scale operation prohibitive. Consequently, users of such systems are tending to utilize such systems to a lesser degree. This is especially disadvantageous in the area of medical imaging, wherein very harmful and undesirable results (in terms of improper diagnosis and increased liability of medical personnel) can be experienced as a result of failure to produce an adequate number of medical images.
Another typical imaging system of the prior art involves a combination of simple optical and complex positioning mechanisms. The theory of operation is similar to that previously described, and is quite simple. A picture is presented on a picture tube CRT (or TV monitor) of contrast and brightness suited to the operator's taste. Light energy is then passed through an objective lens to a flat plane film surface. Typically, the lens has an adjustable focal length and a standard iris F stop device which can be used to limit the amount of light transmitted to the film plane. Such a lens can be so characterized as to decrease the functional error normally experienced due to CRT curvature and other inadequacies in the CRT monitor and the film plane space.
The type of system thus described is a single-format device, that is, a device capable of producing a single image on a single piece of film. To render this particular format as cost effective as possible, manufacturers have developed a Cartesian coordinate system through which the lens travels and stops in particular quadrant spaces.
Other systems have been developed in order to provide a multi-image capability, that is, to facilitate the positioning of plural images on a single piece of film. Techniques to accomplish this have included a rather complex (and costly) mechanical transport system which moves the images through the Cartesian plane, this being accomplished by a simple X-Y positioning network that will move the lens, and therefore move the image on the film. It should be noted that, in such an arrangement, there exists a percentage of error introduced because of lens curvature in relation to film plane space.
In order to maintain a constant aspect ratio for the image, prior art practitioners have developed special arrangements (including electrical circuitry) which will increase or decrease the picture size on the CRT face, thus maintaining the aspect ratio throughout the film plane space as it relates to the pictures taken. For example, the image on the CRT may be a full screen image in single-image format. If the operator then chooses to switch to a multi-image format (for example, six images on one film), the image on the CRT obviously must decrease, thus becoming smaller. Thus, it is necessary to provide means for automatically driving the lens systems away from the CRT face so that the focal distance and the focal point may be maintained as they relate to the film plane space. This involves further expense in the development of such analog systems (the term "analog systems" being utilized to define systems involving such analog-type electronic equipment as TV cameras and CRT's, as well as the various typical techniques described above).
Prior art practitioners have also developed techniques for displaying a calibration pattern between "picture times," the purpose of the calibration pattern being to establish a zero reference point that would be considered white as it relates to the incoming video signal. This establishes an absolute white level in an effort to achieve better reproduction from picture to picture. However, such a technique constitutes an effort to employ state-of-the-art electronics technology to compensate for the inadequacies of or disadvantages produced by mechanical technology, the overall result being increased cost in development and production of the systems in question.
Another prior art practitioner utilizes a system somewhat similar to the above, but less complex in nature (for example, microprocessors are not at all employed). Thus, such a prior art system does not provide the capability of automatic electrical adjustment of various optical parameters, offering instead a uniform contrast and brightness control for both positive and negative images. In addition, the system does not offer an F stop adjustment, and the only exposure control offered is in the realm of brightness. The system employs an X-Y servo-position system which is reasonably accurate, but offers a great deal of optical abrasion at the film plane space.
A further prior art system employs a mechanical drive mechanism, whereby the operator physically moves the film position in a predetermined pattern, which then allows the multi-formatting to be accomplished in accordance with the manual operation. Of course, the disadvantages of such a manual system are quite clear.
To summarize the above discussion of the prior art, it should be noted that such systems of the prior art all display pictures in the analog realm, that is to say, images are displayed on a CRT picture tube, and a lens system is employed to correct, focus and position the image on a film plane space. All such systems utilize a light transmission method of viewing, since such systems employ silver-based negative-type film. Such systems are, accordingly, characterized by several substantial drawbacks: (1) such systems are quite slow, since various different processes (both automatic and manual) must be interfaced; (2) such systems are inaccurate, this being the result of such factors as optical distortion, and lack of accurate and automatic control of brightness, exposure, focus, etc.; (3) such systems produce reproductions of limited quality, the quality of reproduction being limited by the type of film employed, as well as the overall characteristics of the system; (4) such systems employ (as is evident from the above) analog positioning systems which introduce error, involve interface of electrical, mechanical and manual operations, and are quite often very crude in their operation; and ( 5) finally, such systems are costly due to size and complexity, as well as maintenance and over-head associated with operation of the system, especially when the system is operated on a large scale. With respect to lack of quality and accuracy in such prior art systems, if such prior systems were employed in the multi-formatting mode of operation to take a series of six pictures, all pictures being taken from the same original image, and if a densitometer were employed to measure the actual light transmission through the film, a five to seven percent variation in reading would be noted between the various pictures. In certain applications, especially those pertaining to the medical usage of such a system, such a variation in error is intolerable.